Lubricating oil compositions used to lubricate internal combustion engines contain a base oil of lubricating viscosity, or a mixture of such oils, and additives used to improve the performance characteristics of the oil. For example, additives are used to improve detergency, to reduce engine wear, to provide stability against heat and oxidation, to reduce oil consumption, to inhibit corrosion, to act as a dispersant, and to reduce friction loss. Some additives provide multiple benefits, such as dispersant-viscosity modifiers. Other additives, while improving one characteristic of the lubricating oil, have an adverse effect on other characteristics. Thus, to provide lubricating oil having optimal overall performance, it is necessary to characterize and understand all the effects of the various additives available, and carefully balance the additive content of the lubricant.
It has been proposed in many patents and articles (for example, U.S. Pat. Nos. 4,164,473; 4,176,073; 4,176,074; 4,192,757; 4,248,720; 4,201,683; 4,289,635; and 4,479,883) that oil-soluble molybdenum compounds are useful as lubricant additives. In particular, the addition of molybdenum compounds to oil, particularly molybdenum dithiocarbamate compounds, provide the oil with improved boundary friction characteristics and bench tests demonstrate that the coefficient of friction of oil containing such molybdenum compounds is generally lower than that of oil containing organic friction modifiers. This reduction in coefficient of friction results in improved antiwear properties and may contribute to enhanced fuel economy in gasoline or diesel fired engines, including both short- and long-term fuel economy properties (i.e., fuel economy retention properties). To provide antiwear effects, molybdenum compounds are generally added in amounts introducing from about 350 ppm up to 2,000 ppm of molybdenum into the oil. While molybdenum compounds are effective antiwear agents and may further provide fuel economy benefits, such molybdenum compounds are expensive relative to more conventional, metal-free (ashless) organic friction modifiers
U.S. Pat. No. 6,300,291 discloses a lubricating oil composition having a specified Noack volatility containing a base oil of a specified viscosity index, calcium-based detergent, zinc dihydrocarbyldithiophosphate (ZDDP) antiwear agent, a molybdenum compound and a nitrogen-containing friction modifier. The molybdenum compound was used in an amount providing the formulated lubricant with up to 350 ppm of molybdenum. The claimed materials are described as providing fuel economy benefits compared to compositions containing only molybdenum compounds. Despite the foregoing, there continues to be a need for more cost effective lubricant compositions that provide equivalent or superior performance to lubricant compositions without the presence of molybdenum-based friction modifiers.
In accordance with a first aspect, one exemplary embodiment of the disclosure provides an improved lubricating oil composition substantially devoid of molybdenum compounds that may provide equivalent or superior lubricating properties. The lubricating oil composition includes an oil of lubricating viscosity having a viscosity index (VI) of at least about 95; a calcium detergent in an amount introducing from about 0.05 to about 0.6 wt. % calcium into the composition; an amount of a metal dihydrocarbyldithiophosphate compound introducing up to about 0.1 wt. % (1000 ppm) of phosphorus into the composition; at least one titanium compound in an amount sufficient to provide the composition with at least 10 ppm up to about 1500 ppm of titanium. The composition has a Noack volatility of less than about 15% and contains an effective amount of at least one friction modifier.
In accordance with a second aspect, the disclosure is directed to a method of improving the fuel economy and/or the wear characteristics of an internal combustion engine, which method comprises the steps of lubricating an internal combustion engine with a lubricating oil composition of the first aspect and operating the engine.
In accordance with a third aspect, the disclosure is directed to the use of a lubricating oil composition of the first aspect to improve the fuel economy, and/or the wear characteristics of an internal combustion engine.
Other and further objects, advantages and features of the disclosed embodiments may be understood by reference to the following.